The process that leads to successful osseointegration of an implant into the surrounding tissues is a complex one that involves cell migration, attachment, differentiation, proliferation, extracellular matrix synthesis and finally mineralization of that matrix. Implant materials are as biocompatible as their surface chemistry allows for a favorable interaction with the biological molecules relevant for that tissue.
For example, placement of endosseous dental implants has been limited to areas of favorable bone character, and fixtures must remain unloaded after placement for considerable periods of time. The primary challenges faced in the fabrication of new endosseous implants are to increase the rate of osseointegration and the percentage of bone apposition. Histological analysis of integrated titanium (Ti) implants into bone tissue revealed that many clinically successful implants are among 30-60% opposed directly by mineralized bone. The rest of the implant surface has been found to be apposed by fibrous tissue and unmineralized collagen fibers. It is desirable that the entire circumference of the osseointegrated implant be directly apposed by mineralized bone tissue.
Extracellular matrix proteins, especially certain adhesion molecules, play a role in bone repair and morphogenesis. These molecules can modulate gene expression through cell surface-extracellular matrix interactions. The interaction between the titanium oxide layer of dental implants and certain extracellular matrix proteins may be a prerequisite for reproducible direct apposition of bone to titanium implants.
Human osteoblast cell lines undergo a coordinated temporal expression of osteoblast phenotypic markers during their differentiation in vitro and produce a mineralized extracellular matrix. This bone developmental system is ideal for studying the interaction between titanium surfaces and bone cells in vitro.
The implants of the invention are improved implants which increase the rate of osseointegration and the percentage of bone apposition. Implant surfaces should have such properties which permit the phenomenology of the relevant cells. The achievement of reproducible biological integration of implants calls for a delineation of the molecular biological events relevant to the morphogenesis of the desired interfacial tissue. Material surfaces that can not bind the macromolecules supportive of osteoblast function, are not likely to make a good bone implant.
An enhanced rate of osseointegration and/or augmented percentage of bone apposition around implants or cell recruitment systems of the invention increases implant placement indications, expedites loading time, and opens new fields for research in implant materials.
Accordingly, the present invention provides a novel osteopontin containing implant. In an embodiment the coated implant increases the rate of osseointegration and the percentage of bone apposition. The implant of the invention includes a material suitable for use in vivo within a subject in combination with a releasable form of osteopontin forming an osteopontin containing implant.
In another aspect of the invention, the implant includes a material suitable for use in vivo within a subject in combination with at least two osteopontin polypeptides forming an osteopontin containing implant.
In another aspect of the invention, the implant includes a material suitable for use in vivo within a subject in combination with at least two osteopontin active polypeptides, wherein the active polypeptides are attached to the material such that upon implantation into the subject the osteopontin containing implant induces new bone formation.
In yet another aspect of the invention, the implant includes a material suitable for use in vivo within a subject in combination with a releasable form of osteopontin, wherein the osteopontin is attached to the material such that upon implantation into the subject the osteopontin containing implant induces new bone formation.
In still another aspect of the invention, the implant includes a material suitable for use in vivo within a subject in combination with an active osteopontin peptide forming an osteopontin containing implant.
In another aspect the invention features an osteopontin containing titanium implant. The implant includes a releasable form of phosphorylated osteopontin in combination with titanium suitable for use in vivo within a subject forming an osteopontin containing titanium implant.
In yet another aspect the invention features a method of coating an implant with an osteopontin or an active fragment thereof. The method includes non-covalently or electrostatically attaching osteopontin or an active fragment thereof to a surface of an implant, wherein the osteopontin or an active fragment thereof is attached to the surface of the implant such that it is releasable from the surface upon implantation into a subject.
In still another aspect the invention features a method of inducing new bone formation in a subject. The method includes implanting an osteopontin containing implant into a subject, wherein the osteopontin is released from the implant into the subject thereby inducing new bone formation in the subject.
In another aspect the invention features a method of inducing new bone formation in a subject at a site where bone formation is needed. The method includes implanting an osteopontin containing implant into a subject at a site where bone formation is needed, wherein the osteopontin is released from the implant into the site thereby inducing new bone formation at the site.
In another aspect the invention features an osteopontin containing cell recruitment system. The system includes a releasable osteopontin or a fragment thereof in a form which provides a gradient and an implant, forming a cell recruitment system in the proximity of the implant, wherein the implant is targeted for cell recruitment by a gradient of osteopontin which forms in the proximity of the implant.
In another aspect the invention feature a packaged releasable osteopontin or a fragment thereof for use in a cell recruitment system. The package includes a releasable osteopontin or a fragment thereof in a form which provides a gradient in the proximity of an implant which is targeted for cell recruitment by the gradient of osteopontin, packaged with instructions for use of said osteopontin or a fragment thereof with the implant targeted for cell recruitment.
In another aspect the invention features a coated osseointegrator capable of implantation. The osseointegrator includes a coated material which is enhanced for ooseointegration by at least about 100% when compared to an uncoated material based on the human osteoblast cell (HOS) attachment assay.
In another aspect the invention features a coated implant. The implant includes a coated material which increases the proliferation of osteoblasts by at least about 100% when compared to an uncoated material based on the human osteoblast cell (HOS) proliferation assay.
In still another aspect, the invention features a method for inducing new tissue formation in a subject at a site where tissue formation is needed. The method includes adding osteopontin into a subject at a site where tissue formation is needed, wherein the osteopontin induces new tissue formation about the site.
In yet another aspect, the invention features an osteopontin glue which includes osteopontin, a mucopolysaccharide and a multivalent metal, e.g., calcium, magnesium or manganese. Preferably, the osteopontin is at a concentration of about 100 xcexcg/g of glue.